1. Field of the Invention
The present invention relates to an adhesive composition for adhering a rubber and fibers. More particularly, the present invention relates to an adhesive composition for adhering the rubber and reinforcing fibers contained in a rubbery product such as a tire, a belt and a hose.
2. Description of the Related Art
Polyester fiber is widely used as a rubber-rein-forcing fiber in various applications such as carcass cords for radial tires, since it suffers from less elongation and has better dimensional stability than nylon fibers. However, since the polyester fiber has poor heat resistance, its adhesion strength between said fiber and the rubber greatly decreases after vulcanization at high temperature or thermal history at high temperature (heat resistant adhesion strength), and further its adhesion strength after vulcanization between the fiber and the rubber (initial adhesion strength) is poor. Then, the improvement of such adhesion strength is highly desired.
Since nylon or rayon fiber for reinforcing rubber is more active in adhesion with the rubbers than polyester fiber, the former fiber can be adhered to the rubber with an adhesive composition (RFL) comprising a butadiene-styrene-vinylpyridine copolymer latex or a mixture of said latex and a butadiene-styrene copolymer latex, and a resorcin-formalin resin (RF resin) to provide good initial adhesion strength and heat resistant adhesion strength.
In the RFL for the polyester fiber, the butadiene-styrene-vinylpyridine copolymer latex as such or the mixture of said latex and the butadiene-styrene copolymer latex is also used. Since the RFL for the nylon or rayon fiber does not give practical adhesion strength with the polyester fiber, the polyester fiber is pretreated with epoxy resins or isocyanate compounds and then treated with the RFL, or treated with a mixture of the RFL and an adhesive such as VULCABOND (manufactured by ICI Vulnax) wherein the main component is 2,6-bis-(2,4-dihydrophenylmethyl)-4-chlorophenol.
The latex to be contained in the RFL has been also improved. For example, Japanese Patent Kokai Publication Nos. 26629/1986 and 26630/1986 propose the use of a latex of vinylpyridine base copolymer modified with a carboxylic acid or its ester. However, in case of the polyester fiber, the cord strength of the fiber after dipping in said RFL is greatly decreased, and the adhesive composition comprising such latex has poor heat resistant adhesion strength so that the adhesive composition is not satisfactorily used in applications which require good heat resistance.